Note: Descriptions are shown in the official language in which they were submitted.
CA 02485897 2004-10-25
Description:
Brake for a lift
The invention relates to a brake for a lift, which brake consists of two brake
halves,
wherein a compression spring for activation of the brake and an actuator for
release of the
brake are provided for each brake half and wherein compression spring and
actuator act
on at least one active brake lining, which produces a braking force at a brake
surface
when the actuator is deactivated.
A brake device for a hoist frame drivable by means of a linear motor has
become known
from Patent Specification DE 41 06 595, wherein load cells produce a signal
for releasing.
Brakes arranged at the hoist frame embrace the guide rails arranged in the
conveying
shaft, wherein a brake is provided for each guide rail. The brake has a brake
shoe for
each limb side of the guide rail. Actuating elements produce, for each brake
shoe, braking
forces on the guide rail by means of the brake shoe, wherein the action of a
spring
activates the brake and a hydraulic cylinder opposes the spring force and
release the
brake.
A disadvantage of the known equipment resides in the fact that the brake
produces
different braking moments in the case of normal operation and in the case of
failure of a
brake half. In the known brake one brake half generates the necessary braking
moment or
the two brake halves together produce twice the braking moment, which in the
case of
normal operation can lead to slipping of the cable on the drive pulley. The
strands in the
case of a steel cable are, and the casing in the case of a synthetic fibre
cable is, thereby
very highly loaded or excessively worn.
A lift drive with a disc brake, the brake calliper of which is mounted to be
floating, has
become known from Specification JP 04133988. The brake is actuated by means of
a
compression spring and released by means of an actuator acting against the
compression
spring. When the brake is released the brake calliper is moved by means of a
further
compression spring into the initial position.
A disadvantage of the known equipment resides in the fact that in the event of
spring
breakage or wearing away of a brake lining the brake fails.
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Here the invention will provide a remedy. The brake according to the present
invention
fulfils the object of avoiding the disadvantages of the known equipment and of
creating a
brake which has optimised properties with respect to both operation and
safety.
The advantages achieved by the invention are substantially to be seen in that
the
necessary braking moment is maintained and that the double redundancy
necessary for
lift drives is nevertheless guaranteed. The redundancy is maintained even in
the event
of spring failure or wearing away of a brake lining. The brake consisting of
two
independent halves generates the braking moment necessary for normal
operation. In
the event of failure of a brake half the brake according to the invention
nevertheless
generates the necessary braking moment. In the case of a fault the passengers
are
subjected to less high loads and the lift is mechanically loaded to a lesser
degree. In
addition, with the gentler retardation undesired triggering of the safety
brake device due
to the mass inertia of the limiter cable is also avoided. In the case of an
emergency stop,
excessive decelerations do not occur particularly in the case of lift
installations with large
reserves of traction, which in turn preserves the mechanical system and avoids
slipping
of the cable on the drive pulley. The cage position derived from the signal
generator of
the motor shaft is correctly maintained for the control.
In one aspect, the present invention provides a brake for a lift, which brake
consists of
two brake halves, wherein each brake half comprises a compression spring for
activation
of the brake, an actuator for release of the brake, and at least one active
brake lining,
wherein the compression spring and the actuator act on the at least one active
brake
lining, which produces a braking force at a brake surface when the actuator is
deactivated, wherein the brake is mounted to be floating perpendicularly to
the brake
surface, and wherein each brake half further comprises at least one passive
brake lining
and in the case of failure of one of said brake halves, the passive brake
lining acts on
said brake surface instead of the active brake lining of the failed brake
half.
In a further aspect, the present invention provides a method of operating a
brake for a
lift, which brake consists of two brake halves, wherein a compression spring
for
activating the brake and an actuator for release of the brake are provided for
each brake
half and wherein the compression spring and the actuator act on at least one
active
brake lining, which produces a braking force at a brake surface when the
actuator is
deactivated, wherein a same braking force is generated in the case of normal
operation
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2a
and in the case of failure of at least the compression spring of one brake
half, wherein at
least one passive brake lining is provided for each brake half and in the case
of failure of
one of said brake halves, the passive brake lining acts on the brake surface
instead of
the active brake lining of the failed brake half.
In yet a further aspect, the present invention provides a brake for a lift,
comprising a
generally u-shape brake housing with two rigidly connected limbs maintained at
a fixed
spacing from each other, each forming a brake half having an active brake
lining, a
compression spring for activation of the active brake lining and an actuator
for release of
the active brake lining, the compression spring producing a braking force
against a brake
surface located between the limbs when the actuator is deactivated, at least
one fixed
passive brake lining in addition to and independent from the active brake
lining located
on each brake half for pressing against the brake surface by the compression
spring of
the other brake half in the event of a failure of the brake half, and means
for mounting
the brake for floating travel of the brake housing in a perpendicular
direction to the brake
surface for engaging the brake surface with the passive brake lining on the
brake half by
the action of the compression spring of the other brake half in said event of
failure of the
brake half.
The invention is explained in more detail on the basis of the accompanying
figures, in
which:
Fig. 1 shows a schematic illustration of the brake according to the invention
in
normal operation,
Fig. 2 shows a schematic illustration of the brake according to the invention
in
the event of a spring breakage of a brake half,
Fig. 3 shows a side view of the brake according to the invention,
Fig. 4 shows a section along the line A-A of Fig. 3 and
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Fig. 5 shows a plan view of the brake according to the invention.
Fig. 1 shows a schematic illustration of the brake 1 according to the
invention in normal
operation. The brake I consists of a housing 2 which is U-shaped in cross-
section,
wherein a limb of the U corresponds with a brake half 3. The brake halves 3
are of
identical construction. An active brake lining 4 and at least one additional
or passive brake
lining 5 are provided for each brake half 3. In a further variant of
embodiment the
additional brake lining 5 can, as explained further below, be omitted. The
additional or
passive brake lining 5 is arranged at the limb inner side of a housing 2. The
active brake
lining 4 is loaded by a spring force of a compression spring 6. Not
illustrated is an actuator
which is explained further below and which in the activated state opposes the
spring force.
The housing is mounted at a first axis 7 to be floating.
In the case of normal operation the active brake linings 4 act on a brake disc
8' which
serves as brake surface 8 and which is part of a drive pulley 9. Cables 12
guided in cable
grooves 10 of the drive pulley 9 rotating about a second axis 11 move a lift
cage (not
illustrated) or a counterweight (not illustrated) of a lift.
The brake 1 according to the invention can also be arranged at the lift cage
or at the
counterweight, wherein the free limb of a guide rail, for example, serves as
brake surface.
The brake 1 is self-centring and can, thanks to the floating mounting at the
first axis 7,
move about a centre position 13 symbolised by a dot. The possible direction of
movement
of the brake 1 is symbolised by an arrow P1 or by an arrow P2.
Fig. 2 shows a schematic illustration of the brake 1 according to the
invention in the case
of failure of one brake half 3. With, for example, a broken compression spring
6 or
wearing away of the active brake lining 4, the one brake half 3 is
ineffective. The spring
force of the compression spring 6 of the other brake half 3 moves the housing
2 in the
direction symbolised by the arrow P1, wherein the passive brake lining 5 of
the one brake
half 3 comes into contact with the brake disc 8'. The initial position of the
brake 1 is
illustrated by a dashed line. As explained further below, the braking force in
the case of
normal operation is maintained also in the case of failure of a brake half 3.
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Fig. 3 shows a side view or a brake half 3 of the brake 1 according to the
invention. The
active brake lining 4 is arranged centrally and an additional or passive brake
lining 5
arranged at the housing 2 is provided for each brake lining side.
A section along the line A-A of Fig. 3 is shown in Fig. 4. The first axis 7 of
the brake 1 is
arranged at a brake 14 of the drive unit or of the lift cage or of the
counterweight. The
brake 1 is shown in a relieved state and is mounted to be floating, wherein it
can move
along the first axis 7. The compression spring 6 is supported at one end at
the housing 2
and at the other end at an armature plate 15 of a brake magnet 16. Brake
magnet 16 and
armature plate 15 form the above-mentioned actuator. In the illustrated state,
the brake 1
is released, wherein the brake magnet 16 is activated and the armature plate
15 carrying
the active brake lining 4 is attracted and wherein the force of the brake
magnet 16
opposes the spring force of the compression spring 6. In the case of
deactivated brake
magnet 16, the compression spring 6 presses the armature plate 15 together
with the
active brake lining 4 against the brake disc 8', wherein the active brake
lining 4 produces
the requisite braking force. If both brake halves 3 act equally, the brake 1
positions itself in
the centre position 13. In the case of brake halves 3 operating unequally, the
brake 1
displaces, thanks to the floating mounting at the first axis 7, in one or the
other direction
P1, P2.
Fig. 5 shows a plan view of the brake 1 according to the invention, wherein
the one brake
half 3 is cut away. The brake I is shown released. In the case of failure of a
brake half,
the two additional or passive brake linings 5 act instead of the active brake
lining 4.
In a further variant of embodiment the additional brake lining 5 can be
omitted. In the
event of spring breakage, the active brake lining 4 acts in this case as an
additional brake
lining, which then stands against an abutment 2.1 as symbolically shown in
Fig. 1 and Fig.
2. As shown in Fig. 4 and Fig. 5, the brake magnet 16 acts as an abutment.
This brake
variant has redundancy in the case of spring breakage and continues to operate
with the
necessary braking moment. If the entire brake half 3 fails, for example in the
case of
wearing away of the active brake lining 4, the brake 1 fails.
The brake 1 can, for example, also be arranged at the lift cage or at the
counterweight
and, for example, act on a limb of a guide rail. In this case, the limb of the
guide rail takes
CA 02485897 2004-10-25
the place of the brake disc 8'. The brake linings can then act on opposite
sides of the
guide rail as described in detail in EP 0 648 703 B1.
The braking moment in normal operation is calculated according to the
following formula:
Mn=2*Fn*.t*r [1l
Mn: braking moment in normal operation
Fn: braking force (compression spring 6) acting on the active brake lining 4
: co-efficient of friction between active brake lining 4 and brake disc 8'
r: mean spacing of the brake 1 from the centre point of the second axis 11
The braking moment in the case of failure of a brake half 3 is calculated
according to the
following formula:
Mf=(Fn+Fp)*.t*r [2]
Mf: braking moment in the case of failure of a brake half 3
Fn: braking force (compression spring 6) acting on the active brake lining 4
FP: braking force (compression spring 6) acting on the additional or passive
brake
lining 5
: coefficient of friction between active/passive brake lining 4/5 and brake
disc 8'
r: mean spacing of the brake 1 from the centre point of the second axis 11
when Fn = FP, then Mn = Mf.
The braking moment of the brake thus remains the same in the case of normal
operation
and in the case of failure of a brake half 3, assuming r remains constant and
the friction at
the axis 7 can be disregarded.
